Monthly Archives: October 2014

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One of the great targets for backyard astronomers is Jupiter, and spotting its moons, the cloud bands and the Great Red Spot is always a treat. Observations over a few days provides a good view into the dynamic nature of the clouds and the orbits of the Moon. I haven’t yet managed to capture the Great Red Spot on photo, but maybe this fall as Jupiter comes back into view in the evening sky, I should make the effort to spot the GRS. This is because ever since it’s discovery in the 1800s, it has been shrinking in size. And at the current rate, it could be gone all together in as little as 20 years!

Jupiter’s Great Red Spot (1995 and 2014) – NASA

In the last 10 years it has shrunk by 3000km, taken a more circular form and increased its rotational speed. Amateur observations since 2012 have revealed that this phenomenon is even accelerating, shrinking by as much as 930km per year. Current measurements have the GSR now pegged at under 15,000km in diameter.

As we head into the fall, Jupiter will become easier to observe. By December Jupiter will be high in the sky around midnight. On February 6th, Jupiter will be at Opposition, fully illuminated by the Sun and at its closest to the Earth.

The photo in the title bar was taken by me back in September 17th, 2010, only 4 days before its closest approach, which shows that even with a small 80mm scope, quite a bit of detail can be captured when the conditions are right.

Like this:

Photos of open star clusters always appear to be more pleasant when stars have diffraction spikes. But if your telescope does not have support vanes from a secondary mirror you are out of luck. One solution is to simply tape in a cross pattern some string or fishing line over the dew shield. Or you can turn to digital enhancement. Below is a procedure to enhance your photos by digitally adding diffraction spikes using GIMP 2.8. in 8 easy steps! No special plugin or filter required.

Lets try with my image of M45 – Pleiades taken with a Skywatcher 80ED.

M45 – Pleiades Benoit Guertin

The first step is to create a new “brush” in the shape of diffraction spikes. To do this, start with new canvas with a transparent background. In the screen shot below, a new 1000 x 1000 pixel image with Fill with: Transparency

Create new image with transparent background

Then draw a grey straight horizontal line. I’ve used the Pencil Tool to create a thin solid line, 4 pixel width end about 300 pixels length. To ensure a straight line, click once to mark your starting point and holding the SHIFT+CTRL keys click again for the end point. Note that my line isn’t centered, that is because the blur performed in the next step will shift the line to the left.

Draw a gray horizontal line

Next use Motion Blur to create the gradient (Filter > Blur > Motion Blur…) The blur angle must be 0 deg such that it’s in the same direction as the line. In this example I’ve used a blur quantity of 150.

Add motion blur to create the gradient.

Duplicate the layer, rotate by 90deg and align both lines to form a cross. A simple step by step is the following:

Select > All

Edit > Copy

Edit > Paste as > New Layer

Layer > Transform > Rotate 90deg clockwise

Tools > Transform Tools > Move (now align the vertical line to form a cross)

Duplicate, rotate and align both lines

Once both layers align, you can merge them into a single layer.

Merge down to flatten into a single layer

Finally, using the Ellipse Selection Tool, select the cross and Copy to clipboard. This will automatically assign it to the Clipboard Brush (red arrow and box below). Note that I have kept the screenshot of my previous version with the black background in the snapshot below to make it easier to see.

GIMP – Diffraction Spike Creation – STEP 4

We now have a new brush type that can be used to create diffraction spikes with nothing more than a single click. Yay! The Paintbrush will show up as a cross but with dotted line (see red arrow in screenshot below). Size and angle can be adjusted via the Tool Option Box; see below sections with red boxes. I use the Paintbrush tool to create the spikes.

Now have a new brush to create the diffraction spikes

Now it’s time to get down to business and add those diffraction spikes to the stars. Start by opening your astrophoto and duplicating into another layer. This duplicate layer will be blurred and used to transfer the colour information on the spikes.

In the duplicated layer (with the original layer turned off), use a heavy Gaussian Blur (Filter > Blur > Gaussian Blur…) to blend out the colours. In this example, I used a blur value of 60px. As the blurring makes the image darker, use the Curves Tool to bring the brightness back up.

Increase brightness after burring

Result of the blurred layer

Now create a Layer Mask for this blurred layer. Select to initialize the Layer Mask to Layer’s alpha channel.

GiMP – Diffraction Spike Creation – STEP 7

With both the original and blurred layer visible. The blurred layer is selected and the blend Mode is set to Screen. Select to edit the mask of the blurred layer (right mouse-click on the blurred layer), and click on the stars to draw the cross pattern. A diffraction spike should instantly appear! As your Brush is the cross pattern, you will see in dotted lines the size and angle. If you don’t see your cursor, simple adjust the size (ex: 500).

GIMP – Diffraction Spikes Creation – STEP 8

Resulting image after clicking on a few bright stars:

M45 with diffraction spikes added

Try different settings (a larger pen width for the initial cross pattern) or playing with the quantity of blurring and curve adjustment of the blurred layer.

If you have other improvements or suggestions, please share using the comment field below.

Like this:

Found a way to create fake diffraction spikes using GIMP. Process comes down to defining a new brush in the shape of a cross, and then using that brush to create spikes in a new layer. Will post a procedure in the next few days.

Like this:

We are all dependent on the weather, and knowing what Mother Nature has in store for us in the next 24hrs helps our daily routine. Backyard astronomers don’t have the luxury to be setup on top of a mountain range, above the clouds where the air is crisp and dry all the time. Therefore knowing in advance if it’s worth hauling out all your gear for a six-hour deep-sky photo-session or a minimalist setup to scan the planets and the Moon can save lots of frustration.

Using data and forecasting models from Environment Canada specifically tailored for astronomers the site provides a simple chart with past, current and forecasted conditions of various parameters that affect the viewing quality. In the above snap-shot cloud cover, transparency and humidity all indicate bad viewing conditions for Friday and Saturday night. (Boooo…..)

While the data is from Environment Canada, Clear Sky Chart provides coverage for the USA and part of Mexico. On the web site you can select the closest observation site, or request to create your own. If your setup is mobile, you can check the viewing conditions at various locations to see if it’s worth to pack up your gear for a road-trip to a place with less light pollution and better weather.

An Android app is also available for your mobile devices and tablets: Clear Sky Droid, essentially using the same charts and data set.

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Messier 57, also known as the Ring Nebula is an easy target with all sizes of telescopes, even large binoculars. Conveniently located almost midway between the bright magnitude 3 stars Beta and Gamma Lyr, it’s very easy to locate. In the wide field of view photo below, we can clearly see M57’s position with respect to the two bright stars.

Ring Nebula – Messier 57 Planetary NebulaBenoit Guertin

M57 is a small target, therefore not ideal for short focal lengths like my Skywatcher 80ED (600mm focal length). Below is a 1.5x zoom on the nebula itself. The digital zoom was performed by cropping and scaling the aligned sub images, prior to stacking them.

On October 19th a once in a lifetime event will happen. Comet Siding Spring (C/2013 A1) will pass very close to Mars, one tenth the distance of the closest Earth-comet pass. While there is no chance of impact, NASA has moved some of its Mars orbiting satellite to be behind the planet is it passes through the comet’s dust tail in order to protect the equipment.

At predicted magnitude 11, it will be limited to large telescopes with camera or CCD. But its close proximity to Mars will make it an easy target to locate. Unfortunately for North America, the closest approach will take place 2:28pm EDT.

Luckily NASA has setup as dedicate web site leading up to and after the even publish information and photos. The SLOOH telescope will also have a live webcast.

Welcome to a journey into our Universe with Dr Dave, amateur astronomer and astrophotographer for over 40 years. Astro-imaging, image processing, space science, solar astronomy and public outreach are some of the stops in this journey!